Apparatus for Direct Fabrication of Nanostructures

ABSTRACT

An all-additive apparatus for direct fabrication of nanometer-scale planar and multilayer structures that performs “pick-and-place” retrieval and deposition of materials comprises a tip and a controller and transport mechanism configured for causing the tip to acquire a transferable material and deposit at least a portion of the acquired transferable material at a predetermined location onto a substrate, without the use of a bridging medium, in order to directly assemble a structure. The tip may be submillimeter-scale, may comprise a plurality of sub-tips disposed in a predetermined arrangement, and/or may mechanically vibrate. Mechanical vibration of the tip may be monitored. The tip may acquire the transferable material from a reservoir. The assembled structure may be cured on the substrate.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 10/367,616, filed Feb. 14, 2003, now U.S. Pat. No. 7,998,528,which claims priority to and the benefits of U.S. Prov. App. Ser. No.60/357,006, filed on Feb. 14, 2002, the entire disclosures of which arehereby incorporated by reference.

FIELD OF THE INVENTION

The present invention generally relates to the field ofmicrofabrication, in particular, to direct fabrication and imaging ofnanometer-scale structures using a scanning probe microscope, e.g. anatomic force microscope.

BACKGROUND

Nanotechnologies promise to bring about the advent of very small, yetimportant electronic and biological devices with features that are onlya few tens of nanometers across. A variety of nanometer-scale (“nano”)materials, such as carbon nanotubes, nanoparticles, and molecularmemories are being developed. However, improvements in the handling andpatterning of these nanomaterials are necessary before they can becost-effectively incorporated into useful nanodevices such as, forexample, single-electron transistors, high-density gene chips, andterabyte-scale memory systems. These devices require new fabrication andpatterning techniques that far exceed resolution limitations of knownprocessing techniques.

For example, known lithographic methods that are at the heart of modernmicrofabrication, nanotechnology, and molecular electronics often relyon patterning a resistive film, followed by chemical etching of thesubstrate. A variety of such subtractive printing techniques employscanning probe instruments, electron beams, or molecular beams topattern substrates using self-assembling monolayers and other organicmaterials to form sacrificial resistive layers. Known microfabricationtechniques such as photolithography, microcontact printing,micromachining, and microwriting can produce patterns as small as 100nm, but the production of sub-100 nm structures still poses a challenge.

Also, many nanomaterials containing discrete components, e.g. nanotubes,must ordinarily be manipulated and directly assembled onto a surfacewithout the assistance of resists, masks, or etching steps. Furthermore,many organic materials that could be useful in nanoscale devices, suchas DNA and proteins, are easily damaged and, thus, are difficult topattern to form very small structures. Thus, new methods are needed toaddress the challenge of patterning and constructing useful nanoscaledevices.

Since its inception, scanning probe microscopy has proven to be a usefultool for high-resolution imaging of nanoscale structures. The scanningprobe typically includes a cantilever made of silicon having a length ofabout 200 μm. The cantilever has a sharp tip at its end with a radius ofcurvature generally below 10 nanometers. Depending on the imaging modeused, topological features as fine as individual atoms can be resolved.

More recently, it has been shown that the tip of a scanning probemicroscope, such as an atomic force microscope (“AFM”), may be usefulfor the direct assembly of nanostructures. The tip can be very sharp,with only a few atoms located at its apex. A number of techniques thatuse an AFM tip to push very small objects, including atoms,nanoparticles, and nanotubes across a surface to form simple patterns,have been developed. However, the pushing operations are very complex,and construction of useful structures is indirect and oftenprohibitively tedious.

Another process, known as “dip pen nanolithography” (“DPN”), uses an AFMtip to deposit a restricted set of organic molecules onto carefullychosen substrates. Generally, DPN is a nanolithography technique bywhich molecules are directly transported to a substrate. DPN utilizes asolid substrate as the “paper” and an AFM tip (or a near-field scanningoptical microscope tip) as the “pen.” The tip is coated with apatterning compound (the “ink”), and the coated tip is used to apply thepatterning compound to the substrate to produce a desired pattern. TheDPN delivery mechanism involves the formation of an adsorbed watermeniscus around the tip to transfer the ink molecules to the substrate,and the control of the movement of the patterning molecules to thesurfaces on which they are deposited by a driving force to formself-assembling monolayers.

Problems that arise with DPN technology stem from the dependence of thistechnique on the liquid meniscus and chemical affinity of the patterningmaterial to the substrate. For example, the lateral width of the linewritten by the “pen” using DPN is limited by the width of the meniscusformed. The meniscus is subject to variations in the relative humidityas well as chemical interactions between the solvent and the substrate.The size of the meniscus may also affect the rate of the transport ofthe patterning compound to the substrate. Solubility characteristics ofthe “ink” molecules in a given solvent can create difficulty inestablishing a desired line width and a suitable loading concentrationof the ink in the solvent. Furthermore, surface tension characteristicsof different solvents can lead to drip or rapid flow from the penresulting in problems with precise control of the ink application undersome circumstances. Finally, special substrate-liquid interactions andself-assembling chemistries may be necessary to promote the adhesion ofthe molecules to the substrate, limiting the kinds of materials that canbe patterned in this fashion.

Thus, there remains an unresolved need in the art to enable rapid anddirect patterning of arbitrary materials onto arbitrary substrates withnanoscale resolutions.

SUMMARY

It is an object of the present invention to achieve direct depositionand patterning of nanoplanar and multi-structures at the desired preciselocations.

It is another object of the present invention to enable patterning awide variety of materials having useful electrical, chemical,mechanical, and biological properties onto a wide variety of substrates.

It is yet another object of the present invention to provide anefficient and inexpensive method of fabricating nanostructures that doesnot require tedious pushing or pulling of particles or othernanometer-sized objects along the surface of a substrate; and does notrequire special self-assembling chemistries or liquid-substrateinteractions, such as water vapor-initiated menisci, to facilitate thetransfer of molecules from the tip to the substrate.

Accordingly, a high-precision nanoprobe-assisted deposition process,capable of directly assembling planar and multi-layer nanostructures byincrementally building them from materials in a liquid or soft-solidphase, is disclosed herein. Also disclosed herein is an apparatusimplementing such process.

A key aspect of the present invention involves direct assembly of planarand multi-layer structures with nanogeometries by a discrete“pick-and-place” technique using a sharp tip mounted on a bendablecantilever, for example, a tip of a scanning proble microscope such asan AFM. The nanoassembly method of the invention facilitateshigh-resolution direct fabrication of arbitrary materials, many of whichare not amenable to deposition using current probe-based patterning,DPN, or conventional lithography methods. Applications of thenanoassembly system of the invention include, but are not limited to,fabrication of ultra-density gene chips, high-capacity magnetic diskdrives, and single electron transistors.

Unlike probe-based nanomanipulation techniques known in the art thatpush atoms or nanoparticles around on a surface, the nanoassembly methodof the invention enables true “pick-and-place” retrieval and depositionof materials with a wide range of electrical, chemical, and mechanicalproperties. The AFM-assisted nanoassembly method of the invention is anall-additive process that substantially eliminates any waste.Exceedingly small quantities of material, a few thousand atoms at atime, can be picked up by an AFM tip from a reservoir and are thenassembled at a designated construction site on the substrate tofabricate nanostructures without subsequent application of causticchemicals, etchants, and other effluents that are typically used inknown microfabrication methods.

Further, unlike known DPN methods, the present invention provides fordeposition of various materials, e.g. metal nanoparticles, polymers,inks, solvents, organics, semiconductor nanoparticles and dielectricnanoparticles onto a variety of substrates without formation of anadsorbed substrate-material or substrate-tip bridging medium, such as aliquid meniscus of water adsorbed from humid air at the interfacebetween the tip and the substrate. In accordance with the presentinvention, materials can be assembled using reservoirs containingliquids, soft solids, or collections of discrete nano-scale objects,such as nanoparticles, that have no chemical affinity to the substrate.

Throughout the following description, the term “ink” is used togenerally refer to the material being deposited by the nanoassemblysystem to form nanoassembled structures. It should be understood thatthe term “ink” is used to refer to materials that are in either a liquidphase or solid phase or some phase in between (such as a gel or slurry).The term “ink” is also used to refer to a collection of solid discreteobjects such as spheres, balls, nanoparticles, nanocrystals, nanotubes,nanorods, cubes, and tetrahedrons. These solid discrete objects may ormay not be entrained in a gas-phase or liquid-phase fluid. The inkmaterials and nanoparticles, once assembled by the methods of theinvention onto a substrate, are stable and can be used as the foundationof multi-layer nanostructures.

The invention makes use of a very sharp tip to transfer material. Thetip may (but need not be) attached to a flexible medium such as acantilever or spring, and may (but need not) be part of an AFM. Inembodiments in which the tip is mounted to a cantilever, the terms “tip”and “cantilever” are used interchangeably. It is the tip and the mannerin which it is used, rather than the specific mechanism by which it isoperated or mounted, that is important to the invention.

According to embodiments of the invention, the tip is mounted on abendable cantilever, for example, a cantilever of a scanning probemicroscope, such as an AFM, and operates as a manipulator of both liquidand solid materials at nanometer scales. The tip may be controlled aspart of the AFM feedback loop including the following components: anano-scale tip mounted on a bendable cantilever; a sensor that monitorsthe degree of bending of the cantilever and the frequency of itsoscillation (and thereby monitors the forces exerted onto the tip); andan actuator and feedback circuitry that cause the tip to deliver aspecified level of force, impact velocity and/or impulse to thesubstrate. The dimensions of deposited nanostructures can be controlledby adjusting, at least (a) the rate of vibration of the tip; (b) thesharpness of the tip; (c) the viscosity, phase, and material propertiesof the ink; and (d) pressure and force impulse applied by the ink-ladentip to the substrate. For example, with respect to adjusting theviscosity of the ink,

-   -   the smallest depositions are achieved when using very        non-viscous fluids or near-hard solids that are nearly fully        solidified;    -   larger depositions are obtained from more viscous fluids or soft        solids; and    -   the largest depositions are achieved using very viscous        liquid-phase materials.

The resolution of the resulting nanostructures may approach 1 milliondots per linear inch (1 trillion dots per square inch). Depositedvolumes can be precisely controlled to span 10 orders of magnitude, from10⁻²⁴ to 10⁻¹⁴ liters. The nanostructures assembled using the method ofthe invention may have line widths of less than approximately 100 nm,with the smallest discrete circular features being less than 32 nmacross. The method of the invention facilitates creating structures withheight-to-width aspect ratios of better than 1-to-2 and providesimproved control over line width and deposition rate, while beingrelatively insensitive to fluctuations in ambient conditions, such astemperature, humidity, atmospheric conditions, vibration, and thermaldrift. A dot of material can be discretely deposited onto the substrateat rates greater than 1 dot per second.

In general, in one aspect, the invention features a nanoassemblyapparatus that includes a nanometer-scale bendable cantilever having atip mounted thereon; a controller; and a transport mechanism. Thetransport mechanism, responsive to the controller, causes the tip todiscretely acquire a transferable material; scan the tip over asubstrate; and deposit at least a portion of the acquired transferablematerial at a predetermined location directly onto the substrate withouta bridging medium, thereby assembling a nanostructure on the substrate.

In one embodiment, the nanoassembly apparatus also includes one or morereservoirs from which the tip acquires the transferable material.Optionally, the transferable material does not chemically bond to thesubstrate upon deposition thereon. The nanoassembly apparatus may alsoinclude means for facilitating a continuous flow of the transferablematerial to the tip from the reservoir. In yet another embodiment, thetemperature of the reservoir is controlled by the apparatus.

In some embodiments, the tip of the nanoassembly apparatus is ananotube, for example, a carbon nanotube. In other embodiments, the tipis made of silicon.

The controller of the nanoassembly apparatus may include means formonitoring and controlling the forces exerted on the tip. In oneembodiment, the controller also includes an actuator and feedbackcircuitry for causing the tip to apply a predetermined amount of forceto the substrate. In another embodiment, the controller also includesmeans for monitoring a force with which the tip deposits thetransferable material in order to determine an amount of thetransferable material deposited. In yet another embodiment, thecontroller includes means for monitoring a force with which the tipacquires the transferable material in order to determine an amount ofthe transferable material acquired. For example, the controller monitorsa deflection of the cantilever indicative of flooding of the tip andcounteracts the cantilever deflection in response thereto. In yetanother embodiment, the apparatus includes means for detecting floodingof the tip and counteracts this condition by adjusting the position ofthe tip in response thereto.

In one embodiment, the nanoassembly apparatus includes a curing devicefor curing of the transferable material deposited on the substrate, forexample, a laser source, an ultra-violet light source, an electron-beamsource, a heat source, an infra-red light source, an electric currentsource, or an electric voltage source. In one aspect of the invention,the tip comprises the curing device.

In some embodiments, the tip of the nanoassembly apparatus includes aplurality of sub-tips disposed in a predetermined arrangement. Theplurality of sub-tips may simultaneously deposit the transferablematerial in a predetermined pattern onto the substrate in a single step,as well as simultaneously or independently acquire and deposit differenttransferable materials.

In some embodiments, the bendable cantilever and the controller are partof a scanning probe microscope, for example, an atomic force microscope.In one embodiment, the scanning probe microscope of the nanoassemblyapparatus images the nanostructure following the deposition thereof. Inyet another embodiment, the tip images or detects the structure before,during or after deposition of the transferable material.

The tip may be configured for vibration. In one embodiment, the tipvibrates when depositing the acquired transferable material onto thesubstrate. In another embodiment, the tip vibrates when acquiring thetransferable material.

In some embodiments, the controller monitors the shift in a vibrationfrequency and/or vibration amplitude of the tip. Optionally, thecontroller controls the descent of the tip towards the substrate, theamount of the transferable material acquired by the tip, and/or theamount of the transferable material deposited onto the substrate by thetip by monitoring the shift in a vibration frequency and/or vibrationamplitude of the tip. For example, monitoring the vibration amplitudefacilitates control of the tip's descent and/or the amount oftransferable material acquired by (and/or deposited by) the tip.

In general, in another aspect, the invention features a method fornanoassembly that includes the steps of providing a tip mounted on abendable cantilever, causing the tip to discretely acquire a firsttransferable material, scanning the tip over a substrate, and operatingthe tip to deposit at least a portion of the acquired first transferablematerial at a predetermined location directly onto the substrate withouta bridging medium. The method further includes repeating the latterthree steps to create a nanostructure using the first transferablematerial. A resulting nanostructure may be two-dimensional, orthree-dimensional, with at least some of the transferable material beingdeposited onto previously deposited transferable material.

In one embodiment, the method of the invention also includesfacilitating a continuous flow of the transferable material to the tipfrom the reservoir. In another embodiment, the transferable materialdoes not chemically bond to the substrate upon deposition thereon.

The method for nanoassembly may also include monitoring and controllingthe forces exerted on the tip. In one embodiment, the method includescausing the tip to apply a predetermined amount of force to thesubstrate. In another embodiment, the method includes monitoring a forcewith which the tip deposits the transferable material onto the substratein order to determine an amount of the transferable material deposited.In yet another embodiment, the method includes monitoring a force withwhich the tip acquires the transferable material in order to determinean amount of the transferable material acquired. Also, the method mayinclude monitoring a deflection of the cantilever indicative of floodingof the tip and counteracting the cantilever deflection in responsethereto. Also the method may include detecting flooding of the tip andcounteracting this condition by adjusting the position of the tip inresponse thereto. The method for nanoassembly may optionally include thestep of thermal curing of the deposited transferable material on thesubstrate.

In some embodiments, the tip includes a plurality of sub-tips disposedin a predetermined arrangement, and at least a portion of thetransferable material is deposited in a predetermined pattern in asingle step by the plurality of sub-tips.

In one embodiment, the acquiring step also includes causing the tip todiscretely acquire a second transferable material simultaneously withthe first transferable material. The depositing step may includeoperating the tip to deposit at least a portion of the acquired secondtransferable material simultaneously with at least a portion of theacquired first transferable material. In yet another embodiment, the tipacquires a second transferable material before, during, or after the tipacquires a first transferable material. In yet another embodiment, thetip deposits a second transferable material before, during or after thetip deposits a first transferable material. At least a portion of thesecond transferable material may be deposited so as to overlap at leasta portion of the first deposited transferable material.

In some embodiments, the method for nanoassembly includes the step ofcausing the tip to vibrate. In one version of this embodiment, the tipvibrates when depositing the acquired transferable material onto thesubstrate. In another version, the tip vibrates when discretelyacquiring the transferable material.

In one embodiment, the method for nanoassembly includes the step ofcausing momentary contact between the tip and the substrate to deposit adot of the transferable material. In another embodiment, the methodincludes translating the tip along the substrate to deposit a line ofthe transferable material. The line of the transferable material mayhave a width of less than approximately 100 nm, for example,approximately 17 nm.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. The drawings are not necessarilyto scale, emphasis instead generally being placed upon illustrating theprinciples of the invention.

FIG. 1 schematically illustrates the nanoassembly apparatus according toan illustrative embodiment of the invention;

FIG. 2 depicts a vibration isolation system, which may be employed withthe nanoassembly apparatus of FIG. 1;

FIG. 3A depicts the steps of a method for nanoassembly of dottedpatterns according to an illustrative embodiment of the invention;

FIG. 3B depicts the steps of a method for nanoassembly of line patternsaccording to an illustrative embodiment of the invention;

FIG. 3C depicts a “flooding compensation” technique, which may beemployed with the methods for nanoassembly of FIGS. 3A-3B according toanother illustrative embodiment of the invention;

FIG. 4 depicts the steps of a solvent-assisted method for nanoassemblyaccording to an illustrative embodiment of the invention;

FIG. 5 depicts images of sample nanostructures deposited using the“grayscale” method according to an illustrative embodiment of theinvention;

FIG. 6 schematically illustrates a nanoassembly apparatus including alaser curing device according to another illustrative embodiment of theinvention; and

FIG. 7 depicts the steps of a method for nanoassembly using thenanoassembly apparatus shown in FIG. 6.

DETAILED DESCRIPTION

The nanoassembly method of the invention provides for the deposition ofplanar, multi-layer, and three-dimensional nanostructures. Inparticular, the nanoassembly system can be used for the fabrication of anumber of basic canonical structures including lines, dots, and columns.These canonical structures can be combined and adjacently depositedlaterally and/or vertically to form complicated and useful structures,devices, and patterns.

Referring to FIG. 1, in one embodiment, a nanoassembly apparatus 100 inaccordance with the invention includes a controller 105 that operates anAFM head 110 in three dimensions over the surface of a substrate Sdisposed on top of an adjustable substrate positioning stage 111. Asillustrated in FIG. 1, the surface of substrate S extends in the (x,y)plane, while movement toward and away from the surface occurs along thez axis. A transport mechanism may execute movement along the three axesusing a series of independently operable piezo elements, which areunited into a single tube 112. AFM head 110 comprises a bendablecantilever 115, which terminates in a tip 120. In one version of thisembodiment, tip 120 is secured directly to the underside of AFM head 110by way of a magnetic plate angled at a nominal 4.5 degrees relative tosubstrate S. The end of the tip may be submicron in scale, may be lessthan 10 μm across, or may be less than 100 μm across. A piezoelectricoscillator 125, itself operated by a frequency-synthesizer module 127 ofcontroller 105, deflects cantilever 115 as indicated by the arrow as tip120 passes over the substrate S. Alternatively, oscillatory deflectionof cantilever 115 may be provided by one or more piezo elements definingor within tube 112. The instantaneous degree of cantilever deflection ismonitored by a conventional optical arrangement comprising a laser 130,a split-photodiode detector 135, and a detector circuit 140. The outputof detector 140 is fed back to controller 105.

The system 100 also includes a data-handling circuit 150 thatorchestrates nanoassembly operations and facilitates communication withstandard or non-standard computer architectures. An interface module 155sends commands to controller 105, causing tip 120 to be brought adjacenta desired point on substrate S. A data cache 160 directs transfer ofdata about the target structure during nanoassembly, and stores acquiredimage data in read mode. The data, in turn, is received from or sent toan operator equipped with a computer 180 by means of an input/outputmodule 170. In response to the operator's input, computer 180 throughinterface 155 causes the controller 127 to direct appropriate movementand operation of AFM head 110. A source of material 190 to be depositedonto substrate S, for example an ink reservoir, is disposed in closeproximity to the deposition area of substrate S. The ink reservoir canbe located adjacent to, on, or inside tip 120 (or cantilever 115), andthe system may include conventional temperature-regulation circuitry tomaintain the reservoir at a desired temperature. The nanoassemblyprocess proceeds under computer control to dip tip 120 into reservoir190 of a soft solid or liquid ink (unless reservoir 190 is located on orinside tip 120), to then translate the tip to the deposition site, andto then quickly lower tip 120 onto substrate S surface to causedeposition of the ink. In one embodiment of the invention, thenanoassembly apparatus 100 is based on an EXPLORER scanning probemicroscope available from Thermomicroscopes of Sunnyvale, Calif., withNSC12/W2C model tips coated with a conductive layer of tungsten carbideavailable from MikroMasch of Moscow, Russia.

Cantilever 115 of the invention can operate in either of two modes,namely, contact mode and tapping mode (sometimes referred to as“non-contact” mode). In a contact mode, cantilever 115 is not activelydeflected. Instead, the tip 120 contacts substrate S (or a thin layer ofmolecules adsorbed thereon) as it is scanned over the surface.Controller 105 moves AFM 110 head along the z axis in response to thedetector signal in order to maintain a constant cantilever deflection astip 120 is scanned over the changing surface topography. By virtue ofthis feedback loop, the force between tip 120 and the surface remainsconstant. To obtain an image of the topography of a surface, thechanging z-axis position is recorded as the head is scanned over thesurface.

In a “tapping” mode, the form of operation preferred herein, cantilever115 is oscillated at or near its resonance frequency with an amplituderanging, typically, from 1 nm to 100 nm. For example, cantilever 115 maybe 250 μm in length and composed of silicon, with a resonance frequencyof 30-300 kHz; such elements are available from Digital Instruments,Santa Barbara, Calif. Tip 120 lightly “taps” on the surface of substrateS during scanning, contacting (or nearly contacting) the surface at thebottom of its oscillation excursion. The feedback loop comprising thedetector 135, the detector circuit 140, and the controller electronics105 maintains a constant oscillation amplitude by raising or loweringAFM head 110 along the z axis to maintain a “setpoint” amplitude and/orfrequency.

In some embodiments, the tip that is caused to vibrate with frequenciesup to several hundreds of kilohertz is used to both assemble and thenimmediately image the deposited nanostructures. Due to the vibratingaction, the same tip that assembles the nanostructures can go back andscan those nanostructures only moments later, without unintentionallydepositing more material onto the substrate. In such embodiments, theoperator is able to visualize the nanostructures as they are beingconstructed in situ.

The vibrating mode also provides the piezo actuators of tube 112controlling the descent of tip 120 (based, for example, on the vibrationamplitude) with advance warning of the approaching surface S. Theactuators can then compensate to dramatically reduce the impact forcesdelivered by tip 120 to the substrate S, which enables the deposition ofvery high-resolution patterns. Moreover, monitoring the shift in thevibration frequency of tip 120 facilitates accurate real-time measuringof the mass of material gained and lost by tip 120 during each step ofthe pick-and-place process. Based on such measurements, the processparameters can be adjusted in the middle of a run to achieve the optimumdeposition conditions for a range of materials.

To improve accuracy of the microfabrication and imaging of the depositednanostructure, it is desirable to provide vibration isolation tonanoassembly apparatus 100. In one embodiment of the invention, thevibration isolation may be provided by a conventional air-levitatedisolation table, in which the air is supplied from a pressurized tank orcompressor through a regulator. Referring to FIG. 2, in anotherembodiment of the invention, an elastic (or bungee) cord-supportedisolation system 220 provides vibration dampening to the nanoassemblyapparatus 100 while maintaining a small physical footprint. Theisolation system 220 includes a heavy metal plate 230 hanging from asupport 240 by way of two pairs of criss-crossed elastic cords 250.Metal plate 230 serves as the baseplate supporting nanoassemblyapparatus 100. To further restrict movement and improve motion damping,the bottom of plate 230 is connected to (but still suspended above) ametal plate 260 by two pairs of criss-crossed elastic cords 270. In oneversion of this embodiment, plate 260 is heavier than plate 230. Otherconfigurations of vibration isolation system using one or more platessupported by elastic cord arrangements, however, can also be usedwithout deviating from the scope of the invention.

In yet another embodiment of the vibration isolation system,nanoassembly apparatus is placed on top of a multi-layer stack ofdamping materials, for example, two layers of commonly available plasticbubble-wrap placed on top of a single layer of one-half inch thickcarpeting.

Some liquid-phase ink materials used for nanoassembly may quicklyevaporate. Because viscosity fluctuations of the ink material maysubstantially affect the parameters of the deposited structure, it maybe desirable to prevent any phase transformations during deposition.Therefore, it is useful to control the temperature and atmosphericconditions under which the nanoassembly apparatus operates. Stillreferring to FIG. 2, in one embodiment, nanoassembly apparatus 100 isenclosed in an environmental chamber 280, which preferably istransparent to enable visualization, for controlling atmosphericconditions and particle count. In this embodiment of the invention, thenanoassembly process may take place in custom atmospheres, for example,in argon, helium, nitrogen, oxygen, or neon. An in-situ temperaturecontrol device 290, for example, one or more single- or double-stackpeltiers attached to substrate positioning stage 111 using thermallyconducting paste, is used to perform two functions: (1) cool thesubstrate so that the evaporation rate of the ink in the ink reservoiris reduced, thereby extending the length of time available fornanostructure fabrication using liquid phase inks; and (2) heat thesubstrate for thermal curing of deposited nanostructures. In oneembodiment, when substrate S is being cooled by the peltier or othertemperature-controlling device 290, vaporless atmosphere is maintainedin the environmental chamber 280 to prevent condensation of moistureonto the substrate. In one version of this embodiment, dehumidificationof the area surrounding substrate S is achieved by supplying pressurizedargon, nitrogen, or other suitable gas into enclosure 280.

The methods of the invention can be used to assemble materials with awide range of varying properties including nanoparticles (e.g.,conductor or semiconductor nanoparticles) with or without cappinggroups, microparticles, polymers (e.g., nonconductor, conductor orsemiconductor particles), ceramics, ink compositions (e.g., containingnanoparticles and/or nanotubes), gels, oxides, metals, inorganics,solvents, organics, etchants, plating solutions, catalysts,light-curable or light-crosslinkable materials, resists, biologicalcompounds such as genetic and proteomic materials, light-emittingmaterials such as LEDs, OLEDs and light-emitting polymers, andinorganics (hereafter, collectively, “transferable materials”).Essentially any type and phase of the ink material that can becometemporarily adhered to the tip, and can then also become disassociatedfrom the tip thereby allowing the tip to acquire and then deposit thematerial can be used. In one embodiment, gold and silver nanoparticleinks, diluted to reduce viscosity with alpha-terpineol to metalconcentration of about 5-40% by weight, are used. Other inks can also beused, for example, a silicone-based elastomer pre-cursor, such as DOWSYLGARD 184, available from Dow Chemical of Midland, Mich.; a UV-curableclear adhesive, such as NORLAND optical adhesive #72, available fromNorland Products, Inc, of Cranbury, N.J.; a photoresist diluted withalpha-terpineol, such as SHIPLEY SPR 3012 or AZ1518, available fromShipley Company LLC of Marlborough, Mass. The tip of a thin metal wirecan be used to form ink pools as material reservoirs on a suitablesubstrate, such as a silicon wafer or a glass slide. To reduce contactangle and reduce undesirable “flooding” of a cantilever tip upon contactwith the ink, in one embodiment, the ink-laden wire is dragged across tothe substrate to form an elongated oval-shaped pool.

Nanoassembly deposition can be conducted on a variety of substrates,including glass, quartz, plastics, polyimide, Kapton, silicon, and metalfoil. In one embodiment, the nanostructure is deposited onto a siliconwafer.

Operation of the nanoassembly system of the invention involves a largenumber of control parameters and variables. In one embodiment, theinvention utilizes an expert software system that requests desiredfabrication parameters from the user (such as line width, dot size,viscosity of the ink materials, elapsed drying time of the ink in theink reservoir, etc.) and automatically generates script templates forthe computer commands that control many aspects of the nanoassemblyprocess including tip position and velocity, tip dwell time, and impactforces used to pick up and deposit ink materials. Such softwaresimplifies the process of writing new control code to accommodate somechange in nanoassembly fabrication parameters or constraints. Thefunctions implemented by such structure are described below.

Referring to FIG. 3A, in one embodiment, a method for nanoassembly ofdotted patterns using liquid or soft-solid phase inks begins withdipping the tip into a reservoir of ink with the cantilever operating ineither contact mode or tapping mode (STEP 310). The method furtherincludes withdrawing the tip from the reservoir with a small quantity ofink material adhering to the tip (STEP 315). Then, the tip istransported, preferably at a high rate of speed, for example 1 mm/s to 1m/s at a height of several μm above the surface of the substrate to thedeposition site (STEP 320). Following arrival at the deposition site,the tip is lowered and comes into contact with the substrate (STEP 322),thereby depositing the adhered ink material in the form of a dot of ink(STEP 325). Generally, no externally supplied bridging medium, such as ahumidity-initiated water meniscus, is required between the tip and thesubstrate to facilitate deposition of the adhered ink material. Afterthe dot is deposited, the tip is immediately raised from the surface(STEP 330). The method concludes with high-speed levitatedtransportation of the tip back to the ink reservoir (STEP 335). Thecycle is repeated at a high frequency once for every dot that isdeposited. In one version of this embodiment, the method is performed ata frequency of at least one cycle per second.

Referring to FIG. 3B, in another embodiment, a method for nanoassemblyof line patterns using liquid or soft-solid phase inks includes steps310-322 described above. Following the arrival at the deposition site,the tip is lowered until it comes into contact with the substrate, andis subsequently dragged along the substrate causing the tip to leavebehind a trail of ink. When using liquid-phase inks, the possibility ofdeposition of a large undesirable “bulbous” structure at the beginningof the line is typically minimized by using a tip operating undertapping mode instead of contact mode, because the vibration of the tipin tapping mode prevents the ink on the tip from “flooding” thesubstrate (STEP 340). After the line is deposited, the tip isimmediately raised from the surface (STEP 345). The method concludeswith high-speed levitated transportation of the tip back to the inkreservoir (STEP 350).

The nanoassembly system can achieve high-resolution structures bycontrolling a number of variables and parameters. For example,typically, the size of deposited dots and lines is directly proportionalto the sharpness of the tip of the cantilever and the force applied bythe tip to the substrate at the point when the dot is deposited, andinversely proportional to the viscosity of the ink. Also, when the tipis dipped into the ink reservoir and controlled so that the tip engagesthe ink in the reservoir at or near the damped resonance frequency ofthe cantilever-reservoir system, a cantilever operating in a tappingmode typically extracts a smaller volume of ink from the reservoircompared to a cantilever operating in a contact mode, thereby enablingsubsequent deposition of smaller dots onto the substrate. Furthermore, acantilever operating in a tapping mode when depositing the dot upon thesubstrate is capable of providing an advance warning of the approachingsurface as the tip descends to deposit a dot, thereby reducing thetip-to-surface impact force and enabling the deposition of smaller dotsas compared to the cantilever operating in a contact mode.

In some embodiments, when using liquid-phase materials that are composedof solid phases (such as organically capped nanoparticles) within aliquid solvent or carrier, it is desirable to control the viscosity ofthe ink. Specifically, the viscosity of the ink can be reduced by addingmore solvent to the reservoir; maintained by cooling the materialreservoir to hinder solvent evaporation; or increased by heating thematerial reservoir to enhance solvent evaporation and partial thermalcuring. Due to evaporation effects, the viscosity of the materialattached to the tip may change while the tip is transported from thereservoir to the deposition site.

Referring to FIG. 3C, in one embodiment of a method for nanoassemblyusing liquid- phase inks, a “flooding compensation” technique can beemployed to prevent undesirable overloading of the tip with ink thatoccurs when the tip is lowered into the ink reservoir and the inkrapidly traverses the entire length of the cantilever, therebyoversupplying the deposition zone on the substrate under or adjacent thecantilever with a layer of ink. This technique includes the followingsteps:

-   -   (1) the tip is lowered into the ink reservoir (STEP 360) until        it contacts the surface of the liquid-phase ink in the ink        reservoir (STEP 365);    -   (2) as liquid ink begins to “flood” or rush onto the tip from        the ink reservoir, the feedback circuit of the piezo actuator of        the z axis (“vertical motion actuator”) detects the deflection        of the cantilever (when using contact mode) and/or the dramatic        change in resonant frequency and/or amplitude (when using        tapping mode) (STEP 370);    -   (3) to compensate for this deflection and/or change in resonant        frequency and/or amplitude, the vertical motion actuator is        immediately activated to pull the tip farther up out of the        reservoir, thereby preventing the ink from rushing upon the tip        and down the length of the supporting cantilever (STEP 375);    -   (4) by adjusting the integral setting of the feedback loop to        accommodate a number of factors including the viscosity of the        ink and the force setpoint, the tip can resonantly engage the        ink reservoir without flooding to create a standing ripple wave        within the ink reservoir (STEP 380);    -   (5) when the cantilever deflection and/or resonant frequency        and/or amplitude is restored as the tip is withdrawn from the        reservoir, the vertical motion actuator again drives the tip        back down into the reservoir (STEP 385); and    -   (6) a discrete amount of ink is made to adhere to the tip when        the tip is eventually withdrawn from the ink reservoir (STEP        390).

In another embodiment of the invention, a “flooding compensation”technique can be employed to prevent undesirable “deposition flooding”,which occurs when the tip attempts to deposit its load of liquid-phaseink onto a substrate which results in the deposition of a very large dotor the deposition of a line with a large bulbous structure at one end.Flooding compensation techniques can be employed for both contact andtapping modes, but tapping mode usually provides significantly fasterresponse times and more accurately deposited structures.

As mentioned above, in a particular embodiment of the invention, thecantilever operates in a tapping mode (i.e. having a vibrating tip).This mode is characterized by enhanced feedback sensitivity, whichenables the tip to engage the ink reservoir and substrate with reducedforces when extracting ink from the reservoir and depositing the inkonto the substrate, respectively. Reduced forces preserve the sharpnessof the tip and enable the formation of smaller nanostructures. Also, inthe tapping mode, the operator is able to monitor the mass of inktransferred by the tip to and from the ink reservoir and the substratein real time. In particular, the mass of material acquired by the tipduring the reservoir dipping step, and the mass of material deposited bythe tip onto the substrate can be monitored and calculated in real timeby observing the shifts in the tapping mode resonant frequency and/oramplitude of the cantilever to which the tip is mounted.

In one version of this embodiment of the invention, the nanoassemblysystem employs an algorithm for re-adjusting the drive frequency of thevertical motion actuator using the cantilever feedback loop to moreclosely match the resonant frequency of the cantilever (or othervibration element to which the tip is attached), thereby adjusting forthe changes in the cantilever frequency that results from the tipacquiring and losing mass during the dipping, transporting, anddepositing steps. This algorithm includes adjusting frequency sweeps tofind the newly acquired resonant frequency of the cantilever;re-calibrating the scale used to define the desired vibration amplitudeof the cantilever so that the maximum signal derived from the resonantpeak is set to be at full scale; and setting the vertical motionactuator drive frequency to coincide with the cantilever frequency toobtain the maximum resonant response or to obtain a particular desirednon-maximum response.

Various techniques can be employed to enable the tip to acquire the inkin addition to the method recited in step 310 above. In someembodiments, the tip is exposed to a spray, vapor, nebulization, plasma,condensing gas, or powder deposition, of the ink material. Also, anothertip or brush-like or sponge-like instrument may be used to apply ordeposit the ink onto the tip. Furthermore, in yet another embodiment, anink reservoir is located adjacent to or inside or on the tip and/orcantilever so as to enable the ink to move along the outside or throughthe inside of the tip and/or cantilever to reach the extremity thereof.

In still another embodiment, a solvent-laden tip is dipped into thesolid-phase ink in a reservoir via the “solvent assisted” nanoassemblymethod. In this embodiment, solid ink in a reservoir is locally softenedor partially dissolved by a small quantity of solvent transferred by thetip itself to the ink reservoir from a solvent reservoir disposedproximally thereto. Thusly softened or dissolved solid ink is thenextracted from the ink reservoir by the tip, as described above.

In one version of this embodiment, use of a solvent facilitatesextraction of solid-phase ink from a reservoir by the tip in a tappingmode despite the limited forces that can be applied by the tapping modetip to the surface of the reservoir. During the nanoassembly process,the tip is dipped into a first reservoir of solvent and then into asecond reservoir of solid ink before the fabrication of each dot orline. Solvent-assisted techniques according to this embodiment of theinvention facilitate relatively prolonged construction of complex planardesigns, because the duration of fabrication is limited only by theoverall evaporation time of the solvent and not by the evaporation timeof the ink in the ink reservoir. Also, because typical solvents do notchange viscosity during evaporation, many viscosity-related compensationmethods (such as dynamic tuning algorithms) need not be employed duringfabrication. This solvent-assisted technique, which is applicable bothto contact mode and to tapping mode, enables fabrication of relativelylong, substantially uniform lines that can be drawn continuously untilthe solvent runs out or dries out. Alternatively, the solvent can be anyliquid-phase material (such as an etchant) that causes the solid ink inthe reservoir to soften or dissociate or dissolve, so as to becomeadhered to the tip.

Referring to FIG. 4, in a particular embodiment, the solvent-assistednanoassembly method includes the following steps:

-   -   (1) initiating vibration of the tip (STEP 410);    -   (2) dipping the tip into the liquid-phase solvent reservoir and        extracting a small volume of solvent (STEP 415);    -   (3) dipping the solvent-laden tip into the solid-phase ink        reservoir, wherein the solvent immediately begins to soften        and/or dissolve the solid ink in a region near the tip (STEP        420);    -   (4) extracting a small quantity of ink from the ink reservoir        with the tip (STEP 425); and    -   (5) depositing the ink onto the substrate with the tip to form a        dot, line, column, or other desirable nanostructure (STEP 430).

In one version of this embodiment, one or both of the solvent reservoirand the ink reservoir are located adjacent or inside or on the tipand/or cantilever. Also, various techniques can be employed to enablethe tip to deposit the ink in addition to the method recited in steps325 and 340 above. For example, in one embodiment, the extremity of thetip is exposed to an “ink disassociation enhancing” means that assistsin removing the ink from the tip, thereby causing the ink topreferentially adhere to the substrate or other pre-existing structureor pattern on the surface of the substrate. Examples of such meansinclude thermal sources, such as radiation sources, peltiers, hotplates, resistively heated zones, and lasers; light sources for fixinglight-curable materials; cooling sources including refrigeration unitsand peltiers for fixing “freezeable” ink materials; sources of a secondmaterial that help to remove a first ink material from the tip andassist in getting that first ink material to preferentially adhere tothe substrate; and high energy sources located on or in the tipincluding an electron beam emitter or laser.

In one embodiment of the invention, a tip capped with multiple“sub-tips,” located at the extremity of the tip in a specifiedarrangement, is used to simultaneously deposit a complicated pattern ina single deposition step. For example, all of the required components ofa single electron transistor (the gate, source, drain, and Coulombblockade island) can be deposited in one deposition step. In one versionof this embodiment, these multiple “sub-tips” can be located so closelyadjacent to one another as to approximate the topographical features ofa nanostamp. Thus, the tip can be used like a nanostamp, wherein therelief pattern on the end of the tip can be transferred to the substratevia an ink pattern. In another version of this embodiment, multiplesub-tips are used to simultaneously retrieve and deposit different kindsof ink materials.

In one embodiment of the invention, grayscale patterns with varyinglinewidths and dot sizes can be generated by using a single dippingoperation in the ink reservoir followed by two or more consecutivedeposition steps so that the linewidth and dot size decrease withgreater numbers of deposition steps. Referring to FIG. 5, four“grayscale” copies of the letter “N” have been assembled in parallel.Four different line thicknesses were achieved by using a single ink pooldipping operation followed by four consecutive deposition steps, one foreach “N” being constructed. As shown in FIG. 5, dot size is uniform andrepeatable, as demonstrated by a series of grayscale lines that wereformed simultaneously, built up from many dots using grayscale methods.The grayscale method of this embodiment can be employed with bothliquid-phase and solid-phase ink materials.

As mentioned above, in general, dot size can be reduced by altering anumber of parameters including tip force, tapping or contact mode, andviscosity or hardness of the ink material. Dot size can also besubstantially reduced by using a “scratch pad” method wherein the tip isdipped only once into the ink reservoir and is then used to deposit morethan one dot onto the substrate. Excess ink is removed from the tip viathe first several deposited dots (in a separate “scratch pad” locationon or off the substrate). The final dot to be deposited is much smallerthan could normally be obtained (even when using a very sharp tip).Thus, a “scratch pad” zone can be used to “pre-deposit” largernanostructures, followed by precision deposition of much smallernanostructures within the intended fabrication area. This method issimilar to the “grayscale” method described above and shown in FIG. 5,except that the dots deposited in the “scratch pad” zone are discarded.

The scratch pad method can be employed with both liquid-phase andsolid-phase ink materials. With a sufficient number of pre-depositionsteps conducted within the scratch pad zone, a single molecule, a singleatom, or a single nanoparticle may remain at the extremity of thenanotip for subsequent deposition within the intended fabrication area.The scratch pad method allows a tip with a relatively large tip radius(several tens of nanometers in most cases) to deposit a diminishinglysmall dot (approximately 2 nm or smaller) of material onto thesubstrate. Such a small dot of a metal or other conductive orsemiconductive material is particularly useful as the Coulomb blockadeisland in a single electron transistor.

In one embodiment of the invention, the nanoassembly system uses thesame tip for (1) direct deposition of nanostructures; (2) imaging ofthose nanostructures during and after their deposition (i.e. using thescanning probe microscope in its conventional role of generating animage of small-scale topography); and (3) imaging of alignment marksand/or pre-existing structures. The ink material that becomes adhered tothe tip during dipping of the tip into a reservoir of material onlyminimally deteriorates the tip's capability for subsequenthigh-resolution imaging. In one version of this embodiment, imagingresolution is improved by dipping the tip into a reservoir of solvent orlight etchant just prior to the imaging step, thereby removing some orall of the adhered ink material. In an alternative embodiment, adedicated tip is used for imaging during and after the deposition.

According to embodiments of the invention, in-situ imaging of thesubstrate, alignment marks, and pre-existing structures is conductedperiodically during the deposition process to visualize the depositedstructure and adjust the system settings if necessary to compensate, forexample, for relative thermal drift between the substrate and the tipand accumulation of feedback loop control errors.

Many ink materials require curing during or after deposition to obtain astable nanostructure. In a preferred embodiment of the invention, thedeposited structures are cured in-situ without removal of the substratefrom the positioning stage using different curing devices, for exampleheating devices, such as peltiers that are also used for cooling of thesubstrate, as described above, laser sources, ultra-violet or infraredlight sources, electric current sources, electric voltage sources, orelectron-beam sources.

To prevent force-related flattening of the deposited structure afterdeposition and to facilitate construction of three-dimensionalnanostructures, in one embodiment, the invention provides for curing orfusing of newly deposited material (while simultaneously verticallysupporting it with the tip) using an electron beam emitted from the tipof the nanoassembly apparatus. In this embodiment, a curing processcauses a phase transformation at the very instant that the tip comesinto contact with the top surface of the multi-layer structure. The tipremains in contact with the deposited material until the end of thephase transformation, thereby serving as a support for the newlydeposited material to counteract intermolecular and surface forces. Alocal emitted electron beam can be used to cure (i.e., crosslink, fuseor melt) and instantly weld any material that is generally curable,solidifiable, fusible or meltable using electron beam radiation.Examples of such inks include nanoparticle inks, UV-curable polymers,and E-beam-curable polymers. Thus, in this embodiment of the invention,an electron beam emitted from a conductive tip instantly welds newmaterials into place on top of the substrate and/or on top ofpre-existing nanostructures, thereby facilitating construction ofthree-dimensional nanostructures. In this embodiment, high melting pointcoating materials, such as silicon carbide, may be used to provide arobust conductive surface for electron emission from the tip. A suitablerange of a tip-to-substrate current during the electron-beam-assistednanoassembly is between approximately 2 to 20 micro-amps. In one versionof this embodiment, in order to maintain a constant flow of electronsdespite substantial fluctuations in the circuit resistance as the tipmakes and breaks contact with the substrate, a fast-acting currentsource is used as a source of electrons to be supplied to the tip. Inanother version, a voltage source is used. Preferably, the electronsource is triggered on and off by a threshold applied to the forcesignal generated by the deflection of the tip (for contact mode) or theshift in cantilever resonant amplitude/frequency (for tapping mode) asthe tip makes and breaks contact with the substrate. In anotherembodiment, an electron emission source with a relative large(>multimicron) spot size, located on, inside, adjacent, or some distanceaway from the tip, is used to cure the material deposited by the tip.

In another embodiment, a light source, for example a laser ornon-coherent source, such as a medium-pressure mercury lamp, is used tocure light-sensitive materials such as UV-curable optical adhesivesdeposited by the nanoassembly system. Because some light-sensitive inks,such as UV-curable optical adhesives, exhibit exceedingly low vaporpressures and do not readily evaporate or harden at room temperatures,the viscosity or softness of the inks can be kept constant for very longperiods of time without the requirement for the reduced fabricationtemperatures, thereby enabling fabrication of complex patterns over longperiods of time in ambient (humid) environments. UV-curable materialsgenerally include a photoinitiator, i.e. an ingredient that generatesfree radicals, which initiates cross-linking between the unsaturationsites of monomers, oligomers, and polymers. In one version of thisembodiment, a light source located on or near the tip of the cantilevercan be used to intermittently optically cure the deposited materials inthe deposition site each time that the tip moves away from thedeposition site. In another version of this embodiment, a preciselyfocused light source, preferably a laser with small spot size, can beused to cure the light sensitive ink onto the substrate while the tip isstill attached to and temporarily physically supporting the depositedink within the construction zone, thereby enabling the construction ofthree-dimensional nanostructures.

In yet another embodiment, thermally activated tips, for exampleresistively heated zones on the cantilever adjacent to the tip or onapex of the tip, and/or thermally activated substrates, for examplepeltier heated/cooled substrates or regions on the substrate orresistively heated zones on or in the substrate, provide for in situintermittent localized thermal curing of nanostructures at the veryinstant when the nanostructures are deposited by the tip onto thesubstrate or onto other pre-existing nanostructures, thereby enablingthe construction of three-dimensional nano structures.

In yet another embodiment, an integrated laser device, located on ornear or some distance away from the tip, enables in situ intermittentand/or continuous thermal curing, fusing, melting or solidification ofnanostructures while the nanoassembly proceeds. In one version, aninfrared laser-curing device enables in-situ thermal exposure of thedeposited structure at substantial temperatures without removal of thesubstrate from the positioning stage and subsequent re-positioning andalignment during the nanoassembly process (as would normally be requiredfor curing using a large hot-plate or oven). In a second version, alaser device heats the tip (and/or cantilever), which tip then conductsthe heat to the deposited structure. In other words, heating may occurbefore, during or after deposition.

In another version of this embodiment, the laser-curing device isemployed for intermittent thermal curing after deposition of each layerof the structure to obtain a multi-layer structure. For example, a laserwith a relatively large (multi-micron) spot size can be used tointermittently thermally cure the deposited materials in the depositionsite each time that the tip moves away from the deposition site.

In yet another version, a precisely focused and aimed laser with a smallspot size (sub-micron) can be used to weld and/or thermally cure thedeposited ink materials onto the substrate while the tip is stillattached to and temporarily physically supporting the deposited inkmaterial within the deposition site, thereby enabling the constructionof three-dimensional nanostructures.

Referring to FIG. 6, in an illustrative embodiment, a laser curingsystem 600 that is employed with the nanoassembly apparatus 100 includesa laser source 610, a laser source rotating mount 620, a laser beamshutter 630, beam dump 640, focusing lens 650, and a positioningplatform 660. In one embodiment of the invention, a ytterbium fiberinfrared laser, such as the YLD-5000 laser available from IRE-PoulusGroup, emitting at 1060 nm, is used to supply optical power to adeposition site D on substrate S. In one version, the maximum opticalpower supplied is about 5 watts. The near-collimated laser beam isfocused down to illuminate a small fraction of the deposition site D onsubstrate S near tip 115 of cantilever 120 using the focal lens 650positioned proximately to substrate S. In one version of the embodiment,the laser curing system 600 focuses to about a 20×10 μm² spot withindeposition site D. Timed laser beam exposure is provided by the laserbeam shutter 630, for example, a solenoid-driven shutter, placed betweenthe laser source 610 and the focusing lens 650. In one version of thisembodiment, 50 ms long laser bursts were triggered by timing signaloutput during the deposition sequence. In another version of thisembodiment, timed or pulsed laser beam exposure is provided by the laseritself (without assistance from a shutter) to obtain exposure times asshort as femtoseconds. In order to precisely direct the laser beam todeposition site D without thermally affecting the ink reservoir 190disposed nearby, a positioning platform 660 controls the horizontallocation, lateral location, rotation, pitch, and yaw of nanoassemblyapparatus 100 relative to the incoming laser beam. The laser beam sourceis mounted on the rotating mount 620 that provides additional aimingcontrol flexibility. In addition, substrate S is disposed on top ofadjustable positioning stage 111.

Referring to FIG. 7, for laser-assisted nanoassembly, the methods of theinvention described above include a few extra steps at the end of eachdeposition cycle. After the tip extracts inks from the reservoir anddeposits the ink in the deposition site (STEP 710), instead of returningimmediately to the ink reservoir after deposition of the ink, the tip isdirected to move to a “parking location” where it can not be damaged bythe laser beam (STEP 720). Then, the computer controlled shutter opens(STEP 730) and the deposition site is exposed to the laser beam, whichcures the most recently deposited nanostructures in the deposition site(STEP 740). After curing, the shutter is closed (STEP 750); and the tipreturns to the ink reservoir to begin the cycle again (STEP 760).

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the above-describedstructure and methodology without departing from the scope or spirit ofthe invention.

1. Apparatus comprising: (a) a submillimeter-scale tip; (b) a controllerand, responsive thereto, a transport mechanism, configured forrepeatedly (i) causing the tip to acquire a transferable material from areservoir and (ii) pick-and-place depositing at least a portion of theacquired transferable material at a predetermined location onto thesubstrate without a bridging medium, thereby assembling a structure. 2.The apparatus of claim 1, further comprising means for facilitating acontinuous flow of the transferable material to the tip from thereservoir.
 3. The apparatus of claim 1, wherein the tip comprises amaterial selected from the group consisting of a nanotube, a carbonnanotube, and silicon.
 4. The apparatus of claim 1, wherein the tip ismounted on a bendable cantilever and the controller comprises means formonitoring and controlling the forces exerted on the tip.
 5. Theapparatus of claim 4, wherein the controller and transport mechanismfurther comprise an actuator and a feedback circuitry for causing thetip to apply a predetermined amount of force to the substrate.
 6. Theapparatus of claim 4, wherein the controller comprises means formonitoring a force with which the tip deposits the transferable materialin order to determine an amount of the transferable material deposited.7. The apparatus of claim 4, wherein the controller comprises means formonitoring a force with which the tip acquires the transferable materialin order to determine an amount of the transferable material acquired.8. The apparatus of claim 7, wherein the controller monitors adeflection of the cantilever indicative of flooding of the tip andcounteracts the cantilever deflection in response thereto.
 9. Theapparatus of claim 1, further comprising a curing device for curing ofthe transferable material deposited on the substrate.
 10. The apparatusof claim 9, wherein the curing device is selected from the groupconsisting of: laser sources, ultra-violet light sources, electron-beamsources, and heat sources.
 11. The apparatus of claim 1, wherein the tipcomprises a plurality of sub-tips disposed in a predeterminedarrangement.
 12. The apparatus of claim 4, further comprising a scanningprobe microscope comprising the nanometer-scale bendable cantilever andthe controller.
 13. The apparatus of claim 12, wherein the scanningprobe microscope images the nanometer-scale structure followingdeposition thereof
 14. The apparatus of claim 1, wherein the tip isconfigured for mechanical vibration.
 15. Apparatus comprising: (a) a tipcomprising a plurality of sub-tips disposed in a predeterminedarrangement; (b) a controller and, responsive thereto, a transportmechanism configured for repeatedly (i) causing the tip to acquire atransferable material from a reservoir and (ii) depositing at least aportion of the acquired transferable material at a predeterminedlocation onto the substrate without a bridging medium, therebyassembling a structure.
 16. The apparatus of claim 15, wherein theplurality of sub-tips simultaneously deposits the transferable materialin a predetermined pattern onto the substrate in a single step.
 17. Theapparatus of claim 16, wherein the plurality of sub-tips comprises astamp having a predetermined pattern of topographical features.
 18. Theapparatus of claim 15, wherein the plurality of sub-tips simultaneouslyacquires and deposits different transferable materials.
 19. Apparatuscomprising: (a) a mechanically vibrating tip; (b) a controller and,responsive thereto, a transport mechanism for repeatedly (i) monitoringa shift in a vibration frequency of the tip, (ii) causing the tip toacquire a transferable material, and (iii) depositing at least a portionof the acquired transferable material at a predetermined locationdirectly onto the substrate, thereby assembling a structure.
 20. Theapparatus of claim 19, further comprising a reservoir from which the tipacquires the transferable material.
 21. The apparatus of claim 20,further comprising means for facilitating a continuous flow of thetransferable material to the tip from the reservoir.
 22. The apparatusof claim 19, wherein the tip comprises a material selected from thegroup consisting of a nanotube, a carbon nanotube, and silicon.
 23. Theapparatus of claim 19, wherein tip is mounted on a bendable cantileverand the controller comprises means for monitoring and controlling theforces exerted on the tip.
 24. The apparatus of claim 23, wherein thecontroller further comprises an actuator and a feedback circuitry forcausing the tip to apply a predetermined amount of force to thesubstrate.
 25. The apparatus of claim 24, wherein the controllercomprises means for monitoring a force with which the tip deposits thetransferable material in order to determine an amount of thetransferable material deposited.
 26. The apparatus of claim 24, whereinthe controller comprises means for monitoring a force with which the tipacquires the transferable material in order to determine an amount ofthe transferable material acquired.
 27. The apparatus of claim 26,wherein the controller monitors a deflection of the cantileverindicative of flooding of the tip and counteracts the cantileverdeflection in response thereto.
 28. The apparatus of claim 19, furthercomprising a curing device for curing of the transferable materialdeposited on the substrate.
 29. The apparatus of claim 28, wherein thecuring device is selected from the group consisting of: laser sources,ultra-violet light sources, electron-beam sources, and heat sources. 30.The apparatus of claim 19, wherein the tip comprises a plurality ofsub-tips disposed in a predetermined arrangement.
 31. The apparatus ofclaim 24, further comprising a scanning probe microscope comprising thenanometer-scale bendable cantilever and the controller.
 32. Theapparatus of claim 19, wherein the scanning probe microscope images thenanometer-scale structure following deposition thereof.
 33. Theapparatus of claim 19, wherein the tip vibrates when depositing theacquired transferable material onto the substrate.
 34. The apparatus ofclaim 19, wherein the tip vibrates when acquiring the transferablematerial.
 35. The apparatus of claim 19, wherein the controller controlsthe descent of tip towards the substrate by monitoring the shift in avibration frequency of the tip.
 36. The apparatus of claim 19, whereinthe controller controls the amount of the transferable material acquiredby the tip by monitoring the shift in a vibration frequency of the tip.37. The apparatus of claim 19, wherein the controller controls theamount of the transferable material deposited onto the substrate by thetip by monitoring the shift in a vibration frequency of the tip.